The present invention relates to a glass compression molding apparatus.
Conventionally, molding of, for example, an optical glass lens is performed in the manner described below: a glass material which has been melted and solidified beforehand is cut out in a required amount. After the glass material is subjected to grinding or other treatments, it is molded to form a glass preform having a predetermined shape. The glass preform is then introduced into a mold having a high-precision molding shape and then compressed while it is heated at a high temperature. Thereafter, the preform is annealed, and the molded product is then removed from the mold.
In order to heat and anneal the preform effectively, heating and annealing stations are provided, and the mold is moved between the stations.
FIG. 1 illustrates a conventional glass compression molding apparatus.
In FIG. 1, a mold 11 has a bottom die 11a and a top die 11b. A preform 13 is introduced between the bottom die 11a and the top die 11b. The preform 13 is preliminarily shaped by cutting a glass material which has been melted and solidified in a required amount and then grinding or otherwise shaping the glass material. The preform 13 has, for example, a rice ball-like shape. A sleeve 14 is disposed surrounding the bottom die 11a and the top die 11b and extends between the two dies to guide the top die 11b. The mold 11 is caused to slide along a platen 15 having a flat surface.
In a mold introduction station A, the preform 13 is placed on the bottom die 11a, and then the top die 11b is lowered along the sleeve 14, whereby the mold 11 is set. This setting work is done manually.
The mold 11 which has been thus set is automatically moved to a heating station B. In the heating station B, an upper high-temperature hot plate 16 is provided in such a manner as to be movable in the vertical direction, and a lower high-temperature hot plate 17 is buried in the platen 15. When the mold 11 has arrived at the heating station B, the upper high-temperature hot plate 16 moves downward to grip the mold 11 between the two plates 16 and 17. Heat is transmitted from the upper and lower hot plates 16 and 17 through the mold 11 to the preform 13 to heat the preform 13 to 500.degree. C.
Subsequently, the mold 11 is automatically moved to a compression station C. At the compression station C are located an upper high-temperature, vertically movable hot plate 18 and a lower high-temperature hot plate 19 buried in the platen 15. When the mold 11 has arrived at the compression station C, the upper high-temperature hot plate 18 moves downward to grip the mold 11 between the upper and lower hot plates 18 and 19 and thereby heats and softens the preform 13. At that time, the preform 13 is compressed to form a product 20 having a shape corresponding to the cavity of the mold 11.
Next, the mold 11 is automatically moved to an annealing station D. At the annealing station D are located an upper annealing, vertically movable hot plate 21 and a lower annealing hot plate 22 buried in the platen 15. When the mold 11 has arrived at the annealing station D, the upper annealing hot plate 21 moves downward to grip the mold 11 between the upper and lower hot plates 21 and 22. Consequently, the product 20 is annealed to 400.degree. C.
The mold 11 is automatically moved to a mold removal station E. The mold 11 which has arrived at the mold removal station E is manually disassembled to remove the product 20.
In the conventional glass compression molding apparatus of the above-described type, setting of the mold 11 at the mold introduction station A, which is performed by introducing the preform 13 into the mold 11, and removal of the product 20 at the mold removal station E, which is performed by disassembling the mold 11, must be conducted manually, making these steps troublesome and increasing the production cost.
Furthermore, since a large number of mold pairs (for example 10 pairs) are needed, variations in the dimensions of the individual molds 11 or in the maintenance thereof affects the precision of the products 20, making production of products 20 having a consistent quality difficult.
Furthermore, the upper and lower surfaces of the mold 11 readily wear. If foreign matter enters between any combination of the components including the upper high-temperature hot plates 16, 18, the lower high-temperature hot plates 17, 19, the upper annealing hot plate 21, the lower annealing hot plate 22 and the platen 15, the dimensional accuracy of the product 20 deteriorates.
FIG. 2 shows the state of a mold in a conventional glass compression molding apparatus.
In FIG. 2, reference numeral 11 denotes a mold; 11a, a bottom die; 11b, a top die; 18, an upper high-temperature hot plate; 19, a lower high-temperature hot plate; and 23, foreign matter which enters between the bottom die 11a and the lower high-temperature hot plate 19.
The bottom die 11a is inclined due to the presence of the foreign matter 23. Consequently, the upper and lower surfaces of the mold 11 are not parallel and the dimensional accuracy of the product 20 (FIG. 1) suffers.